A relatively new process for making steel, the bottom-blown oxygen steelmaking process developed in Germany, is beginning to receive considerable attention in the United States. This new process has decided advantages over the conventional open hearth process, and even the more recent top-blown basic oxygen process (BOP process) which is currently replacing many open hearth shops. Like the more conventional BOP process, the new bottom-blown oxygen process is a basic process utilizing a combination of an oxygen blow and a lime-containing basic slag to remove the impurities from the molten iron. Unlike the BOP process, however, the bottom-blown oxygen process blows oxygen through tuyeres extending through the vessel refractory lining below the molten metal surface. Each oxygen tuyere is substantially flush with the surface of the vessel refractory lining and is surrounded by a larger concentric tuyere for the simultaneous injection of a protective jacket fluid such as natural gas, propane or other gaseous or liquid hydrocarbons, or at least a fluid containing such hydrocarbons. The hydrocarbon jacket fluid acts in part as a shield between the oxygen or molten metal upon initial emergence into the metal bath thereby momentarily delaying oxidation reactions to prevent rapid errosion of the tuyeres and adjacent refractory material. In addition, the jacket fluid acts as a super-coolant, endothermically dissociating upon contact with the hot molten metal, thereby preventing the rapid increase in temperature that would otherwise result from the oxidation reactions.
Both the BOP and the bottom-blown oxygen processes share a common disadvantage of producing nose-skulls, i.e. build-up of solid material, metal and slag, in the mouth or nose portion of the vessel which eventually restrict the vessel opening and interfere with satisfactory operation of the vessel. Although many mechanical devices have been developed for "deskulling" BOP vessels these are not suitable for bottom-blown oxygen vessels because the nature of the two skulls are quite different. Whereas the BOP skull typically consists mostly of slag, and is therefore friable and easily broken away from the vessel, skulls formed on bottom-blown oxygen vessels are mostly metallic and are very difficult to remove. To remove these nose-skulls, furnace operations are halted, and the skulls torch-cut into pieces and usually recharged as scrap. Because the skulls formed on bottom-blown oxygen vessels are predominately metallic, and form rather quickly, the formation of such skulls does measurably lower metallic yield. In addition, skull removal does often cause damage to the vessel refractories, which must be patched before resuming operation.